1. Field
The present invention relates generally to a tool delivery system and more particularly to a method and apparatus for remotely delivering a tool to the interior of a heat exchanger tube.
2. Related Art
In pressurized water reactor nuclear power plants, steam generator heat exchangers convert the thermal energy of water from the reactor core to steam to drive turbine electric generators. In order to transfer the heat while maintaining separation between the high pressure water that flows through the reactor core and the lower pressure water that is converted to steam, steam generators are constructed of thousands of small diameter tubes which provide a large surface area for heat transfer. The number of tubes in a steam generator typically ranges from about 4,000 to 15,000. Some steam generators utilize straight length tubes each about 60 feet (18.3 meters) long. Most of the steam generators are constructed of U-shaped tubing or long vertical sections with two 90 degree bends joined by a shorter horizontal length of tubing. All the tubes terminate in a thick plate, commonly known as a tube sheet, with an array of holes drilled in it that capture the ends of the tubes and interface with a channel head that forms the inlet and outlet plenums for the primary coolant from the reactor core. During plant operation, the high pressure water that flows through the reactor core transports some amount of radioactive particles through the steam generators and some particles become deposited on the interior surface of the tubes. After plant operation, the steam generators become a source of radiation.
Periodic inspection with eddy current probes is widely utilized to ensure the structural integrity of the steam generator tubing. Due to the elevated radiation fields within the steam generators, robotics and remote controlled motorized devices are used to position and translate eddy current probes through the tubes. The cost of equipment, labor, plant down time and the benefit of minimizing personnel radiation exposure make it highly desirable to optimize the performance and capability of the eddy current inspection process.
The inspection is performed by pushing spooled probes located outside the steam generator through a flexible conduit into a steam generator plenum in the channel head to the robotic manipulator which then routes the probe in a tube of the steam generator. Current systems typically use only a stiff shaft to push the probe through the conduit and tube. These systems are prone to jamming, making the inspection difficult. A few systems use an open air jet directed at the tube end to move the probe through the tube, but the resultant probe driving force is small and the jet of air tends to disperse radioactive contamination making the method undesirable.
Accordingly, it is an object of this invention to provide an eddy current delivery system that will ease passage of an eddy current probe through a delivery conduit and through a heat exchange tube with a minimum of resistance.
It is a further object of this invention to provide such a delivery system that can be deployed efficiently and will minimize the spread of radioactive contamination.